Laser welding has been commonly used to permanently join devices made with plastic. For example, laser welding is commonly used to join together separate plastic bodies to make a larger overall device. One type of laser welding is laser transmission welding (LTW). In laser transmission welding the laser beam passes through a first plastic body and welds at the interface with second plastic body. As such, laser transmission welding requires that the first plastic body be transmissive to the laser beam. This is a significant limitation on the type of plastics that can be used and the location of the welds.
Another type of laser welding is laser absorption welding (LAW). In laser absorption welding both plastic bodies are directly exposed to the laser. Thus, laser absorption welding does not require the use of transmissive plastic to facilitate welding. However, because the laser absorption welding is performed directly on exposed surfaces the technique can cause excessive evaporation and oxidation of the plastic where the laser impacts the surfaces. The damage caused by evaporation and oxidation can be reduced by limiting the power of the laser, but such a reduction in power can also result in reduced welding depth and insufficient bond strength.
Thus, there is a continuing need for improved techniques for laser welding of plastics that can provide improved bond strength while reducing the potential for damage to the surfaces the devices being welded.